Fill valve height problem

Today I installed a new ballcock, the Fluidmaster Fill Valve. All is fine and dandy except one thing. Even at its highest setting, it still leaves much less water in my tank than the previous unit.

So I was wondering if there are any known solutions? For instance, does anyone make an extension platform that acts like a bigger washer? Or, and I don't know the physics of flotation well enough, but would perhaps weighting the floater cut off do the trick?

Am sure I must be asking something that has been asked a million times before.

Please, if it's not obvious by my post, I am a layman, so please leave me any answers using words and terms I can understand ;-)

I hope you know that the stem or housing has a lock nut at the base that can be loosened . Then you lift the entire shaft to have a different level of water

Click to expand...

This is what I thought, but I am almost sure that the platform at the base of the shaft was SOLID, and not a screw. This is why I named the manufacturer of the ballcock, in case someone knew somethign specific about it.

Truth is in the end I'll have to empty is all again, and look, just hoping that someone can give me a specific answer before I do it all again. Being a layman I am extra scared of breaking something. Once I finished, and realized there are no leaks, etc. I am so reluctant to go back in ;-)

At the base of the ballcock (inside the tank), there should be a white collar. It does not look like a lock nut, but thats what it should be

Click to expand...

Going by the box, and documentation, the collar on the inside appears to be solid and physically part of the shaft. I call it the collar, but if I had to say the piece of what I am talking apart, it's the part that goes flush against the washer at the inside of the tank.

Tomorrow morning I will take it apart and look for real, but If I am right, and it is solid, (I already opened the shaft to its maximum) are there any extention solutions? Or weighting the floating value?